I. Field of the Invention
The present invention relates to internal combustion engines and, more particularly, to an eight cylinder horizontally opposed internal combustion engine with a four throw crank shaft having means to reduce engine vibration.
II. Description of the Prior Art
Horizontally opposed internal combustion engines conventionally include an elongated crank shaft which is rotatably mounted within the engine housing. This crank shaft includes a number of crank pins which are radially spaced from the axis of the rotation of the crank shaft for attachment to the piston connecting rods.
The previously known horizontally opposed engines, and particularly eight cylinder engines with four throw crank shafts, are typically balanced for the primary shaking force caused by the engine combustion and piston reciprocation. Conversely, these engines are unbalanced for the yawing couple or moment generated by the rotation of the crank shaft. This yawing couple is generated by the reciprocation of the opposed pistons in opposite directions. Although the pistons exert an equal force in opposite directions on the crank shaft, thus balancing the shaking force, these forces are exerted on the crank shaft at axially spaced positions, thus creating a yawing couple which, in effect, exerts a twisting force on the crank shaft about an axis perpendicular to its rotational axis and causes engine vibration. This yawing couple can be internally balanced for twelve and sixteen cylinder opposed piston engines, but cannot be internally balanced for eight cyinder opposed piston engines having a four throw crank shaft. In such engines, two aligned pistons share a common crank shaft throw.